Prosthetic valves have been used for many years to treat cardiac valvular disorders. The native heart valves (i.e., the aortic, pulmonary, tricuspid, and mitral valves) serve many critical functions in assuring the forward flow of an adequate supply of blood through the cardiovascular system. These heart valves can be rendered less effective by congenital malformations, inflammatory processes, infectious conditions, or disease. Such damage to the valves can result in serious cardiovascular compromise or death. For many years the definitive treatment for such disorders was the surgical repair or replacement of the valve during open-heart surgery. Such surgeries are highly invasive and are prone to many complications, however. Therefore, elderly and frail patients with defective heart valves often go untreated. More recently a transvascular technique has been developed for introducing and implanting a prosthetic heart valve using a flexible catheter in a manner that is much less invasive than open-heart surgery.
In this technique, a prosthetic valve is mounted in a crimped state on the end portion of a flexible catheter and advanced through a blood vessel of the patient until the prosthetic valve reaches the implantation site. The prosthetic valve at the catheter tip is then expanded to its functional size at the site of the defective native valve, such as by inflating a balloon on which the prosthetic valve is mounted.
Another known technique for implanting a prosthetic aortic valve is a transapical approach where a small incision is made in the chest wall of a patient and the catheter is advanced through the apex (i.e., bottom tip) of the heart. Like the transvascular approach, the transapical approach can include a balloon catheter having a steering mechanism for delivering a balloon-expandable prosthetic heart valve through an introducer to the aortic annulus. The balloon catheter can include a deflectable segment just proximal to the distal balloon to facilitate positioning of the prosthetic heart valve in the proper orientation within the aortic annulus.
The above techniques and others have provided numerous options for high operative risk patients with aortic valve disease to avoid the consequences of open heart surgery and cardiopulmonary bypass. While devices and procedures for the aortic valve are well-developed, such catheter-based procedures are not necessarily applicable to the mitral valve due to the distinct differences between the aortic and mitral valve.
For example, compared to the aortic valve, which has a relatively round and firm annulus (especially in the case of aortic stenosis), the mitral valve annulus can be relatively less firm and more unstable. Consequently, it may not be possible to secure a prosthetic valve that is designed primarily for the aortic valve within the native mitral valve annulus by relying solely on friction from the radial force of an outer surface of a prosthetic valve pressed against the native mitral annulus. Also, the mitral valve has a complex subvalvular apparatus, e.g., the chordae tendineae and papillary muscles, which is not present in the aortic valve and which can make placement of a prosthetic valve difficult.
Known prosthetic valves for the mitral valve typically include anchoring devices on the outside of an annular frame to assist in anchoring the prosthetic valve to surrounding tissue. Such anchoring devices can limit the ability to crimp the prosthetic valve, which can increase the overall crimp profile of the prosthetic valve. Prior art anchoring devices also tend to increase the rigidity of the prosthetic valve in the crimped state, which can limit the ability to flex/steer the delivery catheter within the patient's vasculature. Moreover, prior art anchoring devices also can be difficult to position at their desired anchoring locations due to the presence of the subvalvular tissue.
Thus, a need exists for transcatheter prosthetic mitral valves that overcome one or more of these disadvantages of the prior art.